Problems writing on shared pdf after zoom upgrade

I teach a remote class using Zoom. After upgrading to the newest version of Zoom last week, I’m experiencing significant problems with annotating pdfs. There is a huge lag, and after a while the annotations don’t show up at all. It doesn’t seem to be as much of a problem when I annotate on the whiteboard.

I use a desktop MAC to share the pdf, and an iPad to write on.